The invention relates to a drive for a tail rotor on a helicopter which uses a dynamoelectric machine.
A helicopter normally has two rotors, wherein a main rotor is driven by a vertically oriented shaft and a tail rotor by an axially oriented shaft. Here, the term rotor is to be understood as the rotor blades together with the rotor head to which these rotor blades are attached. For helicopters, the aim is to achieve a comparatively high specific power, that is kilowatts/kilogram, in order to increase the load bearing capacity of the helicopter.
A helicopter is an aircraft which starts and lands vertically, and which uses one or more motor-powered rotors for lift and forward motion, these working as rotating lift surfaces or wings or rotor blades, for which reason helicopters are classified as rotary wing aircraft.
With the single rotor systems most commonly used a torque arises at the rotor axis of the main rotor, which causes the body of the helicopter to rotate in the opposite sense. In order to prevent this, one of the possibilities is to provide a sideways counterthrust from a tail rotor.
The tail rotor configuration is a widely used method of construction in helicopters for compensating for the torque produced by the main rotor. With this, a tail rotor, which is attached to a tail boom on the helicopter outside the sweep of the main rotor, creates a horizontal thrust to counteract the rotation of the body about the vertical axis. Apart from torque compensation, the tail rotor also serves to steer the helicopter about its main axis, that is to turn to the right/left. The thrust from the tail rotor is generally controlled by a linkage, which changes the common angular setting of the rotor blades. The tail rotor takes up about 20% of the total drive power of a helicopter.
A disadvantage of drives previously used for a tail rotor is that a comparatively high proportion of the drive power and the total weight of the helicopter is due to the tail rotor.
In order to compensate for the torque, a helicopter with double rotors is known from WO 09/143669 A1, the rotors on this being driven by electric motors.
DE 39 15 526 A1 discloses a duplex electric motor by which a hollow rotor is set in rotation from outside and from inside, so that a comparatively high power can be achieved relative to conventional electric motors.
DE 198 56 647 A1 discloses a high-torque electric motor which is constructed as a multi-pole permanent-magnet-excited electric machine and has a hollow cylindrical rotor made of mild steel, which has permanent magnets positioned on both sides, is arranged coaxially between an outer and an inner stator and has a rotatable linkage to a shaft mounted in a bearing in the machine housing.